This proposal concerns a psychophysical analysis of spectral (wavelength) mechanisms in human perifoveal vision, especially those subserving interactions between rod-and cone-initiated signals. Despite advances in the study of foveal spectral mechanisms, they have not been addressed systematically outside the fovea. This analysis will reveal how photoreceptor signals combine and interact in the processes of visual detection and adaptation. The results are of particular importance to understanding color processing, visual adaptation, post-receptoral pathways, and cone-rod interactions in perifoveal vision. Upon completion, there will be estimates of the minimum number of mechanisms, their spectral sensitivities, the extent to which they are independent, unitary, or interactive, the nature of rod influence, their dependence on spatial and illuminance parameters, whether they are spectrally opponent, and their similarity to foveal mechanisms. Threshold-versus-intensity (TVI) functions, along with tests of curve shape invariance and displacement laws, reveal the number of mechanisms and the degree of their independence. Field sensitivity functions, derived from the TVI functions, will reveal the spectral sensitivities of light adaptation mechanisms. Test sensitivity functions will define the spectral sensitivities of detection mechanisms and the corresponding spectral range over which each mechanism is active. Test- and field-additivity and test-wavelength discrimination procedures will define the degree of spectal opponency of these mechanisms. Variation of test and background parameters will define the spatial dependence of the mechanisms. Manipulation of prior adaptation conditions will allow assessment of spectral mechanisms both when scotopic influences are eliminated and maximized. Analogous foveal tests will allow comparison to the mechanisms found at 7 degrees.